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<head>
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 300px;
        }

        .aside {
            width: 100px;
            height: 150px;
            float: left;
            background: black;
        }

        .main {
            overflow: hidden;
            height: 200px;
            background-color: red;
        }
    </style>
</head>

<body>
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    <div class="aside"></div>

    <div class="main"></div>
</body>

</html>